Actuation system for an active element in a rotor blade

ABSTRACT

In accordance with one embodiment of the present application, an actuation system is configured for actuation of an airfoil member with a flap mechanism. The actuation system can include an upper drive tape and a lower drive tape, each partially wrapped around a first bearing and second bearing. An inboard frame can be actuated by at least one linear actuator. Similarly, an outboard frame can be actuated by at least one linear actuator. The inboard frame is coupled to the upper drive tape, while the outboard frame is coupled to the lower drive tape. An actuation of the inboard frame and outboard frame in a reciprocal manner acts move a flap input lever reciprocally upward and downward. A flap mechanism is configured to convert the movement of the flap input lever into rotational movements of the airfoil member.

BACKGROUND

1. Technical Field

The present application relates to an active element actuation system for a rotor blade.

2. Description of Related Art

It can be desirable to implement an actively controlled aerodynamic member on a rotor blade to improve rotor blade performance during aircraft operation. One conventional design uses a push/pull rod connected to a bell crank on a trailing edge flap. Such a configuration can have several undesirable limitations. For example, the bell crank can penetrate the profile of the rotor blade, thereby negatively increasing the drag. Further, rod end elements can have high coulomb friction and produce an uneven stick-slip motion. Even further, wear over time can eventually produce backlash from mechanical slop between the actuator and the flap, thereby reducing controllability of the flap. Even further, conventional designs can include a potential single point failure, such as a ball screw on an electromechanical actuator, which is susceptible to a mechanical jam.

Hence, there is a need for an improved actuation system for an active element on a rotor blade.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the system of the present application are set forth in the appended claims. However, the system itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side view of an aircraft having a rotor blade with an active flap, according to one example embodiment;

FIG. 2 is a perspective view of the rotor blade with the active flap, according to one example embodiment;

FIG. 3 is a perspective view of an actuation system and a flap mechanism for actuating the active flap, according to one example embodiment;

FIG. 4 is a perspective view of the actuation system, according to one example embodiment;

FIG. 5 is an exploded view of the actuation system, according to one example embodiment;

FIG. 6 is a top view of the actuation system, according to one example embodiment;

FIG. 7 is a partial cross-sectional view of the actuation system, taken at section lines 7-7 in FIG. 6, according to one example embodiment;

FIG. 8 is a partial cross-sectional view of the actuation system, taken at section lines 8-8 in FIG. 6, according to one example embodiment;

FIG. 9 is a perspective view of the inboard frame, according to one example embodiment;

FIG. 10 is an exploded view of the inboard frame, according to one example embodiment;

FIG. 11 is a perspective view of the flap mechanism, according to one example embodiment;

FIG. 12 is a top view of the flap mechanism and the actuation system, according to one example embodiment; and

FIG. 13 is a partial cross-sectional view of the flap mechanism and the actuation system, taken at section lines 13-13 in FIG. 12, according to one example embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the system are described below. In the interest of clarity, all features of an actual implementation may not be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.

Referring now to FIG. 1 in the drawings, a rotorcraft 101 is illustrated. Rotorcraft 101 has a rotor system 103 with a plurality of rotor blades 105. The pitch of each rotor blade 105 can be managed in order to selectively control direction, thrust, and lift of rotorcraft 101. Rotorcraft 101 can further include a fuselage 107, anti-torque system 109, and an empennage 111.

Referring now also to FIG. 2, an example rotor blade 105 is illustrated in further detail. Rotor blade 105 has a root end 102, a tip end 104, a leading edge portion 106, and a trailing edge portion 108. Each rotor blade 105 can include a flap 113 that is actively actuated by an actuation system 115. Actuation system 115 is configured to selectively actuate flap 113 so as to provide enhancements of over fixed rotor blade geometry designs, such as: vibration reduction, acoustic reduction, and improved aerodynamic performance. Actuation system 115 is lightweight, compact, wear resistant, and powerful, thereby realizing benefits of an active rotor blade.

It should be appreciated that rotorcraft 101 is merely illustrative of a wide variety of aircraft that can implement the systems discloses herein, such as actuation system 115 for actuating an airfoil member on a rotor blade. Other aircraft implementations can include hybrid aircraft, tilt rotor aircraft, unmanned aircraft, gyrocopters, and a variety of helicopter configurations, to name a few examples. Further, trailing edge flap 113 is merely illustrative of a wide variety of moveable airfoil members that can be actuated with actuation system 115 and flap mechanism 117. For example, a leading edge droop is another illustrative moveable airfoil surface that can be actuated with actuation system 115. Further, it should be appreciated that a plurality of actuation systems 115 may be employed on a single rotor blade 105.

Referring now also to FIG. 3, actuation system 115 can be operably associated with a flap mechanism 117. Flap mechanism 117 is configured to receive inputs from actuation system 115 and mechanically convey the inputs to trailing edge flap 113, while also reacting centrifugal forces subjected upon trailing edge flap 113 during operation, as discussed further herein. Even though flap mechanism 117 is illustrated in conjunction with actuation system 115, flap mechanism 117 can be implemented on a rotor blade having an actuation system that is different from actuation system 115.

Referring now also to FIGS. 4-8, actuation system 115 is described in further detail. Actuation system 115 can include an inboard frame 119 operably associated with linear actuators 123 a and 123 b. Similarly, actuation system 115 can include an outboard frame 121 operably associated with linear actuators 123 c and 123 d. It should be appreciated that an alternative embodiment of actuation system 115 can include a fewer or greater number of linear actuators. In the interest of clarity, linear actuator 123 a is further described; however, it should be appreciated that linear actuators 123 b-123 d are preferably identical to linear actuator 123 a. Further, inboard frame 119 is substantially similar to outboard frame 121, as such, in the interest of clarity, redundant features between frame 119 and frame 121 may only be discussed with regard to one or the other.

Linear actuator 123 a can include a stator 137 having a plurality of conductive windings, and a forcer 139 having a plurality of magnets. Forcer 139 can be linearly displaced at a selected frequency and magnitude by a control system that selectively applies a control signal to stator 137. Forcer 139 is rigidly coupled to frame 119, thus linear translation of forcer 139 similarly translates frame 119. It should be appreciated that linear actuator 123 a is merely illustrative of a wide variety of linear actuators that can be suitable for generating linear motion with suitable displacement and frequency characteristics. For example, linear actuator 123 a can be a linear motor, pneumatic cylinder, or pneumatic muscle, to name a few.

The stator portion of linear actuator 123 a can be located in a housing 141 that is configured to secure stator 137 relative to the internal structure of rotor blade 105. Further, housing 141 can be configured as a heat sink so as to provide a conductive path for removing heat generated by linear actuator 123 a. As such, housing 141 is preferably made from a heat conductive material, such as aluminum, for example.

A plurality of heat pipes 143 can used to provide efficient heat transfer from housing 141 to an exterior surface of rotor blade 105. Each heat pipe 143 includes an evaporator end 147 and a condenser end 145. The evaporator end 147 is in thermal contact with housing 141. Thermal grease can be used to promote thermal contact between the evaporator end 147 and housing 141. The condenser end 145 is in a thermal path with a rotor blade structure such that heat can be transferred to an exterior surface of rotor blade 105.

During operation, each heat pipe 143 transfers heat from housing 141 to an exterior surface of rotor blade 105, where the heat can dissipate into the ambient air. Further, airflow over the exterior surface of rotor blade 105 acts to further remove heat via convection.

Each heat pipe 143 is formed at an angle such that operational centrifugal forces promote condensed fluid to travel from condenser end 145 to evaporator end 147. The angle in each heat pipe 143 is formed by a bend located approximately mid-length of heat pipe 143. The angle of the bend is configured so that condenser end 145 can approximately conform and have maximum contact area with the exterior surface structure rotor blade 105. Further, the angle of the bend in each heat pipe 143 is also configured so that evaporator end 147 can have maximum contact area with housing 141. The thickness and camber of rotor blade 105 can affect the specific angle of the bend in heat pipe 143. For example, a rotor blade having a small thickness between upper and lower airfoil surfaces may have a smaller bend angle, as compared to a rotor blade having a large thickness between upper and lower airfoil surfaces. The unique location and orientation of heat pipes 143 allows for the utilization of centrifugal forces to overcome the undesirable force of gravity and promote the return of the condensed working fluid from condenser end 145 to evaporator end 147.

Actuation system 115 can further include linear bearing assemblies 149 a-149 d to support inboard frame 119 and outboard frame 121 against each housing 141 of linear actuators 123 a-123 d, while reducing friction during the relative linear translation therebetween. Further, each linear bearing assembly 149 a-149 d is configured to prevent increased friction due to operationally generated spanwise centrifugal forces. Even though linear bearing assemblies 149 a-149 d are illustrated, it should be appreciated that linear actuators 123 a-123 d can be moveably supported against frames 119 and 121 using any variety of suitable configurations, such a bearings, gears, slidable elements, to name a few examples.

Inboard frame 119 is reciprocally driven by actuators 123 a and 123 b acting in unison. If one of actuators 123 a or 123 b were to fail, the remaining healthy actuator can provide continued operation while overcoming the slight parasitic drag of the failed actuator. Similarly, outboard frame 121 is reciprocally driven by actuators 123 c and 123 d acting in unison. However, actuation system 115 is configured such that actuators 123 a and 123 b translate inboard frame 119 in an opposite direction to the translation direction of outboard frame 121 by actuators 123 c and 123 d, the translations being in an oscillatory manner, as discussed further herein.

An extension 151 of Inboard frame 119 is coupled to an upper drive tape 125. Similarly, an extension 153 of outboard frame 121 is coupled to a lower drive tape 127. Upper drive tape 125 and lower drive tape 127 can be metal tapes that elastically deform when bent around a pulley. Upper drive tape 125 and lower drive tape 127 are configured to withstand very high frequency motion bending cycles. It should be appreciated that upper drive tape 125 and lower drive tape 127 can be of any material or combination of materials that are able to withstand a high number of bending cycles. For example, upper drive tape 125 and lower drive tape 127 can be formed with 17-7 TH1050 stainless steel and have a thickness of approximately 0.004 inch.

Referring in particular to FIGS. 7 and 8, a first end portion of upper drive tape 125 is coupled to a second bearing 131 such that a portion of upper drive tape 125 is in contact with a radial surface of second bearing 131. The second end portion of upper drive tape 125 is coupled to a lower portion 163 b of coupler 135. Upper drive tape 125 is in contact with a radial portion of first bearing 129 before partially wrapping around a radial portion 155 of coupler 135 and being coupled to a lower portion 163 b. Similarly, a first end portion of lower drive tape 127 is coupled to second bearing 131 such that a portion of lower drive tape 127 is in contact with a radial surface of second bearing 131. The second end portion of lower drive tape 127 is coupled to an upper portion 163 a of coupler 135. Lower drive tape 127 is in contact with a radial portion of first bearing 129 before partially wrapping around radial portion 155 of coupler 135 and being coupled to a upper portion 163 a. It should be appreciated that even though first bearing 129 and second bearing 131 are illustrated as cylindrically shaped, first bearing 129 and second bearing 131 can have other shapes, such as a cam shape, for example. First bearing 129 and second bearing 131 preferably are positioned to place upper drive tape 125 and lower drive tape 127 in tension. Upper drive tape 125 and lower drive tape 127 are configured so that they don't physically overlap each other. In the illustrated embodiment, openings in upper drive tape 125 and lower drive tape 127 allows each to partially wrap around first bearing 129 and attach to coupler 135 without contacting each other.

During operation, inboard frame 119 is actuated reciprocally in directions 159 a and 159 b, while outboard frame 121 is actuated reciprocally in directions 161 a and 161 b. A translation of inboard frame 119 in direction 159 a causes coupler 135 to be pulled in an upward direction 163 a by upper drive tape 125. Conversely, a translation of outboard frame 121 in direction 161 a causes coupler 135 to be pulled in a downward direction 163 b by lower drive tape 127. A ratio between a radius R1 of radial portion 155 of coupler 135 and the outer radius of first bearing 129 forms the mechanical advantage of the transmission of actuation system 115. In such a configuration, linear actuators 123 a-123 d move the flexible drive tapes 125 and 127 which directly displaces the flap input lever 133 that is coupled to coupler 135. The magnitude and frequency of the reciprocal translations of frames 119 and 121 can be selectively controlled during operation.

One advantage of the configuration of actuation system 115 is that inboard frame 119 and outboard frame 121 translate in opposite chordwise directions such that the inertial forces reactions cancel each other, resulting in a system that is not adversely affected by chordwise accelerations of the rotor blade that can occur during operation of the aircraft. For example, lead/lag accelerations are an example of chordwise accelerations of the rotor blade that can be manifest during operation of the aircraft. The unique configuration of actuation system 115 allows it to be substantially unaffected by such lead/lag accelerations.

Referring now also to FIGS. 9 and 10, inboard frame 119 is illustrated in further detail. It should be appreciated that outboard frame 121 is substantially similar to inboard frame 119, and that for the sake of conciseness only inboard frame 119 is shown in FIGS. 9 and 10. Inboard frame 119 is configured to have considerable stiffness and strength to react operational loading and prevent the operational loading from manifesting as deflection where extension 151 is coupled to upper drive tape 125. Deflection of inboard frame 119 could otherwise distort upper drive tape 125 during operation, so as to undesirably reduce the fatigue life of upper drive tape 125.

Inboard frame 119 can be an assembly of composite members and layers configured for rigidly transferring linear displacements of actuators 123 a and 123 b to upper drive tape 125. Inboard frame 119 can include a full pocket 193 and a partial pocket 195 sized to accommodate actuators 123 a and 123 b, thereby forming a brace member 201 extending between arms 203 a and 203 b. It should be appreciated that inboard frame 119 can be modified to accommodate a greater or fewer number of actuators. In an alternative embodiment, inboard frame 119 can include a full pocket in lieu of partial pocket 195, thereby forming an additional brace member.

Inboard frame 119 can include an upper plate 177 and a lower plate 179, each having multidirectional fibers embedded in a resin matrix. A center plate 181 can be located at the center between upper plate 177 and lower plate 179. Tracks 185 a-185 d are formed with unidirectional fibers wound in a racetrack pattern thereby forming full pocket 193 therewithin. Similarly, tracks 187 a-187 d are formed with unidirectional fibers wound in a racetrack pattern, but subsequently trimmed in half to form the geometry of partial pocket 195. An outer member 183 can be included around the exterior. Upper shoe layer 197 and lower shoe layer 199 are formed with unidirectional fibers wound in a racetrack pattern, but also subsequently trimmed to form a horseshoe shaped layer.

Extension 151 can include a filler 191 enclosed by a shell 189. In the illustrated embodiment, filler 191 is a closed-cell foam filler that is trimmed to the desired shape. Shell 189 is a multidirectional composite member that encloses filler 191 to form a rigid torsion box. Shell 189 and filler 191 are butt jointed to outer member 183. Upper plate 177 and lower plate 179 add rigidity by providing a shear support path between torsion box shell 189 and tracks 185 a-185 d and tracks 187 a-187 d.

It should be appreciated that even though extension 151 forms a trapezoidal shape cross-section shape, extension 151 may be configured in other shapes that also perform rigidly in torsion and bending. For example, extension can form a square or rectangular shape.

Inboard frame 119 and outboard frame 121 are configured to act stiff in torsion and bending so that operational loading does not result in deflection at extension 151. Deflection of extension 151 is undesirable because it could result in a wrinkling of upper drive tape 125 and lower drive tape 127, thereby reducing fatigue life.

Referring now also to FIGS. 11-13, flap mechanism 117 is described in further detail. Flap mechanism 117 can include a clevis 165 that is rigidly coupled to flap 113. Clevis 165 slidingly engages flap input lever 133 such that rotational inputs from flap input lever 133 result in rotational movements of flap 113 about a hinge axis 167. Clevis 165 is configured such that spanwise operational loads, such as centrifugal forces, are not reacted between clevis 165 and flap input lever 133. Rather, centrifugal forces are reacted by a tension-torsion member 171 that is support by an inboard support 173 and an outboard support 175. Inboard support 173 is fixed relative to rotor blade 105. In the illustrated embodiment, inboard support 173 is coupled to a fixed portion of a hinge assembly 169. Outboard support 175 is fixed relative to flap 113. During operation, tension-torsion member 171 is compliant in torsion to allow for the relative rotation between flap 113 and rotor blade 105. Furthermore, tension-torsion member 171, under tension, stretches in the spanwise direction when reacting centrifugal loads that act upon flap 113. In such a configuration, neither clevis 165, flap input lever 133, nor hinge assembly 169 react the centrifugal loads. Hinge assembly 169, as well as any other hinges between flap 113 and rotor blade 105, is configured with slack in the spanwise direction so that a spanwise movement of flap 113 is not reacted by hinge assembly 169, or other hinges defining hinge axis 167. One benefit is that this configuration of flap mechanism 117 prevents centrifugal loads from causing a spanwise deflection of flap input lever 133 and coupler 135, thereby preventing an undesired wrinkling of upper drive tape 125 and lower drive tape 127.

In the illustrated embodiment, tension-torsion member 171 is a composite band member with fiberglass fibers oriented unidirectionally along the lengthwise axis in a racetrack type configuration; however, the exact composite material and fiber orientation is implementation specific. It should be appreciated that tension-torsion member 171 can be manufactured with a variety of suitable materials. Furthermore, alternative embodiments of tension-torsion member 171 can include mechanical assemblies configured to react centrifugal loads while being compliant in torsion. Such an alternative embodiment can include a cylindrical rod assembly having a bearing, such as an elastomeric bearing, that exhibits the desired tension and torsion properties.

During operation of rotorcraft 101, a control system is configured to command actuation system 115 to actuate flap 113 at a desired frequency and displacement. Actuation system 115 is configured to provide angular displacement of flap 113 of up to positive 10 degrees and negative 10 degrees, for example. Further, actuation system 115 is configured to provide actuation frequencies at least from zero to 30 hertz, for example. The angular displacement and frequency can be continuously changed during operation. Further, actuation system 115 can be operated to provide a large angular displacement at a low frequency (such as once per blade revolution) and low displacements at a high frequency (such as 6 times per blade revolution). The displacement and frequency can be continuously adjusted to achieve one or more desirables, such as vibration reduction, aircraft hover performance, aircraft speed performance, and/or aircraft fuel efficiency, to name a few examples.

The systems of the present application include one or more significant advantages over conventional systems, such as: 1) the actuation system has high bandwidth and large displacement; 2) the actuation system has frames that move in opposite directions so as to negate chordwise loading of the rotor blade; 3) the flap mechanism allows the spanwise position of the flap to float, thereby preventing centrifugal loading from being reacted by the actuation system; 4) the actuation system does not protrude from the normal aerodynamic profile of the rotor blade; 5) the actuation system has a long fatigue life; 6) the actuation system and flap mechanism are scalable to larger and smaller rotor blades; 7) the actuation system can incorporate multiple actuators for redundancy; and 8) the actuation system is resistant to the formation of backlash.

The particular embodiments disclosed above are illustrative only, as the system may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Modifications, additions, or omissions may be made to the apparatuses described herein without departing from the scope of the invention. The components of the system may be integrated or separated. Moreover, the operations of the system may be performed by more, fewer, or other components.

Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the application. Accordingly, the protection sought herein is as set forth in the claims below.

To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. §112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim. 

The invention claimed is:
 1. An actuation system configured for actuating a moveable airfoil surface on a rotor blade, the actuation system comprising: a first bearing and a second bearing; an upper drive tape and a lower drive tape each coupled to the second bearing, the upper drive tape being elastically deformable and at least partially in contact with the first bearing and the second bearing, the lower drive tape being elastically deformable and at least partially in contact with the first bearing and the second bearing; a first linear actuator and a second linear actuator; an inboard frame operably associated with the first linear actuator, the inboard frame being coupled to the upper drive tape; an outboard frame operably associated with the second linear actuator, the outboard frame being coupled to the lower drive tape; and an input lever coupled to the upper drive tape and the lower drive tape; wherein a reciprocal translation of the inboard frame and the outboard frame results in a movement of the input lever.
 2. The actuation system according to claim 1, further comprising: a coupler configured to couple the input lever to the upper drive tape and the lower drive tape.
 3. The actuation system according to claim 1, wherein the first linear actuator is an electric actuator having a stator and a forcer, the stator being fixed relative to the rotor blade while the forcer is fixed relative to the inboard frame.
 4. The actuation system according to claim 3, further comprising: a heat pipe configured for removing heat from the stator.
 5. The actuation system according to claim 1, wherein the first bearing and the second bearing are cylindrically shaped bearings.
 6. The actuation system according to claim 1, wherein the upper drive tape is a flexible metal tape.
 7. The actuation system according to claim 1, wherein the input lever is configured to provide a rotational input to the moveable airfoil surface.
 8. The actuation system according to claim 1, wherein the moveable airfoil surface is a trailing edge flap.
 9. The actuation system according to claim 1, further comprising: a linear bearing located between the linear actuator and the inboard frame, the linear bearing allowing relative movement between the inboard frame and a fixed portion of the linear bearing.
 10. The actuation system according to claim 1, further comprising: a control system for commanding the first linear actuator and second linear actuator to translate the inboard frame and the outboard frame in opposite reciprocating directions.
 11. The actuation system according to claim 1, further comprising: a third linear actuator operably associated with the inboard frame; and a fourth linear actuator operably associated with the outboard frame.
 12. A rotor blade for a rotorcraft, the rotor blade having an actuation system configured for actuating a moveable airfoil surface on the rotor blade, the actuation system comprising: a first bearing and a second bearing; an upper drive tape and a lower drive tape each coupled to the second bearing, the upper drive tape being elastically deformable and at least partially wrapped around an upper surface of the first bearing and the second bearing, the lower drive tape being elastically deformable and at least partially wrapped around a lower surface of the first bearing and the second bearing; a first linear actuator and a second linear actuator; an inboard frame operably driven by the first linear actuator, the inboard frame being coupled to the upper drive tape; an outboard frame operably driven by the second linear actuator, the outboard frame being coupled to the lower drive tape; and an input lever coupled to the upper drive tape and the lower drive tape; wherein a reciprocal translation of the inboard frame and the outboard frame results in a movement of the input lever.
 13. The rotor blade according to claim 12, further comprising: a coupler member configured for coupling the upper drive tape and the lower drive tape to the input lever.
 14. The rotor blade according to claim 13, wherein the coupler member is adjacent the first bearing.
 15. The rotor blade according to claim 13, wherein the coupler member has a radial portion for which the upper drive tape and the lower drive tape at least partially wrap around.
 16. A method of actuating a moveable airfoil surface on a rotor blade, the method comprising: providing a frame member coupled to a drive tape, the drive tape being operably associated with a first bearing and a second bearing, the drive tape being elastically deformable and at least partially wrapped around a first arcuate surface of the first bearing and a second arcuate surface of the second bearing; providing an input lever coupled to the drive tape; reciprocally actuating the frame member in a chordwise direction with a linear actuator so that the drive tape also translates in the chordwise direction, which thereby actuates the input lever in an upward and a downward direction.
 17. The method according to claim 16, further comprising: using a control system to selectively dictate a frequency and a displacement of the actuating of the frame member with the linear actuator.
 18. The method according to claim 16, further comprising: actuating a second frame member associated with a second linear actuator and a second drive tape, the second frame member being actuated in an opposite direction from the frame member. 